One example of a conventional refrigeration equipment that includes a vapor compression refrigeration circuit is an air conditioner that is employed to provide air conditioning for buildings or the like. This type of air conditioner primarily includes a heat source unit, a plurality of user units, and a refrigerant gas junction line and a refrigerant liquid junction line that serve to connect these units together. The refrigerant gas junction line and the refrigerant liquid junction line of the air conditioner are positioned so as to connect the heat source unit and the plurality of user units, and thus the lines are long and have a complex line shape that includes many curves and branches along the length thereof. Because of this, when the air conditioner is to be renovated, there will be many occasions in which only the heat source unit and the user units are renovated, and the refrigerant gas junction line and the refrigerant liquid junction line of the preexisting device are left in place.
In addition, many conventional air conditioners use an HCFC refrigerant such as R22. The lines, devices, and the like that form the refrigerant circuit of this type of air conditioner have a strength that corresponds to the saturation pressure of the operating refrigerant at a normal temperature. However, because environmental problems are being taken into consideration in recent years, there are continuing efforts being made to replace HCFC refrigerants with HFC or HC refrigerants. Because of this, air conditioners that are employed to air condition buildings or the like are being renovated by replacing the preexisting heat source unit and the user units that use R22 as the operating refrigerant with devices that use HFC refrigerants such as R407C that approximate the saturation pressure characteristics of R22 as the operating refrigerant, and reusing the refrigerant gas junction line and the refrigerant liquid junction line of the preexisting air conditioner.
On the other hand, it is desirable for the aforementioned air conditioner to have improved refrigeration efficiency and reduced power consumption. In order to meet these needs, using HFC refrigerants such as R410A and R32 that have saturation pressure characteristics that are higher than those of R22 or R407C has been considered. However, if one attempts to use a refrigerant such as R410A or R32 as the operating refrigerant, not only will the heat source unit and the user units have to be replaced, but the refrigerant gas junction line and the refrigerant liquid junction line will also have to be replaced with lines that have strengths corresponding to the saturation pressure characteristics thereof, and thus the task of installing the air conditioner will be more burdensome than before.
An example of an air conditioner that is capable of solving these types of problems is the air conditioner disclosed in Japanese Published Patent Application No. 2002-106984. This air conditioner has a refrigeration circuit that includes a compressor, a heat source side heat exchanger, and user side heat exchangers, and a heat source side auxiliary heat exchanger that is connected in parallel to the heat source side heat exchanger. When the refrigerant pressure on the discharge side of the compressor of the air conditioner increases during cooling operations, the refrigerant on the discharge side of the compressor is introduced into the heat source side auxiliary heat exchanger and condensed, and thus the refrigerant pressure of the refrigerant circuit between the discharge side of the compressor and the user side heat exchangers (including the refrigerant liquid junction line) can be decreased. This allows the heat source unit and the user units to be replaced with those that use R410A as the operating refrigerant, and allows the refrigerant liquid junction line of the preexisting air conditioner that employs R22 and the like to be left in place and reused.
However, when pressure is increased in the aforementioned air conditioner, the condensing ability of the refrigerant will temporarily increase and an increase in the discharge pressure of the compressor will be suppressed by operating the heat source side auxiliary heat exchanger, and thus when the condensation temperature of the refrigerant in the heat source side heat exchanger or the heat source side auxiliary heat exchanger cannot be sufficiently reduced, the pressure of the refrigerant that flows from the heat source side heat exchanger to the user side heat exchangers (including the refrigerant liquid junction line) can be reduced to the maximum allowable operating pressure of the refrigerant liquid junction line or lower, but there will be times when the refrigerant can only condense to the saturated state or the gas-liquid state. Because of this, the cooling ability of each user unit may decline.
In addition, as noted above, not only will there be situations in which the preexisting refrigerant gas junction line and the refrigerant liquid junction line of an air conditioner that used R22, R407C, and the like will be left in place and reused and a new heat source unit and user units that use the refrigerant such as R410A, R32 as the operating refrigerant, and the like having saturation pressure characteristics that are higher than those of R22 and R407C will be used with the preexisting lines, but there will also be situations in which refrigerant gas junction lines and the refrigerant liquid junction lines that have high saturation pressure characteristics such as R410A, R32, and the like cannot be prepared, even when a new air conditioner is to be installed. In these situations as well, it will be necessary to protect against a decline in cooling ability in each user unit when the refrigerant condensed in the heat source side heat exchanger is reduced in pressure and sent to the user side heat exchangers.